Heretofore pharmaceutical capsule shells (hereinafter "capsules") have been made almost exclusively from gelatin. In a carefully controlled process, metal pins of the desired dimensions are dipped into an aqueous solution of gelatin and then slowly withdrawn, the gelatin coating thus deposited, when dried, forming one half of a capsule. To achieve uniformity in the capsules, the gelatin should be as pure and uniform as possible, the solution used for the dipping should be at a carefully controlled concentration, viscosity and temperature and the pins should be at the proper temperature and should be withdrawn at rate corresponding to a predetermined schedule.
Gelatin, being a natural product, varies in molecular weight and viscosity, depending on its source and previous history, and it is becoming increasingly difficult to obtain adequate supplies having the necessary purity and uniformity. Many other water-soluble polymers, such as cellulose ethers, have been proposed to replace gelatin but none has been commercially successful.